1. Field of the Invention
This invention pertains to semiconductor devices and, more particularly, to a method and apparatus for applying adhesively coated tape material segments; i.e., decals, to leadframes for semiconductor devices, particularly including "Lead-Over-Chip" type semiconductor device assemblies.
2. State of the Art
In semiconductor manufacture, a single semiconductor die (or chip) typically has a lower surface, the back of the die, being devoid of circuitry located thereon. Each semiconductor die also has an opposite upper surface, the active surface or face of the die, having integrated circuitry constructed thereon which is electrically accessible via wire bonding pads located thereon. The wire bonding pads may be arranged in a variety of configurations on the active surface of the semiconductor device, such as along the center of the die, the edges of the die, both, etc.
Typically, a leadframe is used to connect the wire bonding pads of the semiconductor device via wire bonds to other electronic circuitry.
A conventional leadframe and semiconductor device assembly or packaging process employs an adhesive layer to attach the semiconductor device to the die paddle of the leadframe while the lead fingers of the leadframe extend to and terminate adjacent the peripheral edges of the semiconductor device. Typically, the adhesive used to attach the semiconductor device to the die paddle is an epoxy acrylic silicone of polyamide material.
Alternately, a lead-over chip, also sometimes referred to as a lead-on-chip, (LOC) leadframe is used to provide lead fingers to be electrically connected to the bond pads of the semiconductor device through wire bonds thereto and to support the semiconductor device by being adhesively secured to the active surface thereof and, subsequently, encapsulated. An LOC type semiconductor package is described in U.S. Pat. No. 4,862,245 (Pashby et al.).
Typically, in an LOC semiconductor device assembly, the active surface of the semiconductor device is adhesively attached to the underside of the lead fingers of the leadframe through the use of a double-sided, adhesively coated tape having a thermosetting adhesive thereon, although a thermoplastic adhesive may also be used if desired. That is, the adhesively coated tape has thermosetting adhesive coated on both sides thereof and is attached to the underside of the leadframe fingers and the active surface of the semiconductor device using heat and pressure. If necessary, an oven may then be used to further cure, the adhesive. After the adhesive is cured securing the lead fingers in position on the active surface of the semiconductor device, the leadframe is transferred to a wire bonding machine where the bond wires are connected to the bond pads on the active surface of the semiconductor device and to the lead fingers of the leadframe.
Prior to attaching the semiconductor device to the leadframe using an LOC configuration, the adhesively coated tape must be placed onto a heated leadframe that will secure the semiconductor device to the leadframe but will allow access to the bond pads of the semiconductor device. Typically, a single piece of LOC tape is distanced from a continuous roll of tape and cut, using a punch, into two tape segments, i.e., decals, that are spaced apart and cut away to provide access to the bond pads of the semiconductor device. In such an LOC configuration, the continuous strip of leadframes to which the adhesively coated tape is to be applied at die sites thereon is moved perpendicularly to the direction of feeding of the continuous roll of tape from which the tape is cut and applied to the die sites of the leadframe. In such an instance, a single punch is typically used to cut the tape from the continuous roll of tape and apply the cut tape to the die site of an individual leadframe in a one-punch operation where the tape is fed orthogonally with respect to the feeding and movement of the leadframes. The leads of the die site of the leadframe to which tape is applied by the punch are, in turn, positioned such that the tape segments are located adjacent each other on the leads of the leadframe at the die site, such leads extending orthogonally on the leadframe with respect to the movement of the leadframe through the punch assembly.
Such a process suffers from the problem that LOC tape is an expensive material and a large amount of tape is wasted during formation of the LOC tape pieces. With a conventional LOC tape punching apparatus as described hereinbefore, the width of the tape must be large enough to punch two pieces of tape with a space therebetween for the bond pads of the semiconductor device. Therefore, typically, the pieces of tape are cut from the center of a continuous length of tape having a width that is larger than required for the individual pieces of tape. Additionally, the tape cut out for the area where the bond pads of the semiconductor device are located is also waste. In some prior art systems, as much as seventy-five percent (75%) of the tape may be wasted in the cutting and application of pieces of tape to a leadframe, such as an LOC leadframe.
Since adhesive tape used for the LOC type semiconductor device assembly, or any leadframe design which requires the use of tape thereon, is relatively expensive and the misapplication of the tape during the manufacturing process can produce problems in the subsequent automated manufacturing processes, in turn, imposing increased costs, a method for efficiently applying adhesive tape where desired on a leadframe is desirable. Particularly, it is desirable to have tape applied to a leadframe without wasting tape and without having to apply the tape in a single punch operation to the desired die site of the leadframe.